Stream class driver for computer operating system

ABSTRACT

A stream class driver for use in a computer operating system functions together with a minidriver. The minidriver is associated with a particular design for an adapter, which is a hardware device that generates or receives streaming data. The stream class driver deals with common operating system tasks such as direct memory access, scatter/gather memory use and Plug n Play. The stream class driver is independent of the hardware design and can therefore function with any type of streaming device or external buses such as USB or IEEE 1394. The minidriver functionality is limited to only those functions required by the unique aspects of the hardware and for the minimum requirements of operation, thereby minimizing the complexity and burden of designing minidrivers for hardware devices.

This application is a continuation of application Ser. No. 08/994,674,filed Dec. 19, 1997 now abandoned.

TECHNICAL FIELD OF THE INVENTION

The present invention pertains in general to computer software operationsystems, and more particular to a driver for a class of devices whichgenerate or receive streaming data.

BACKGROUND OF THE INVENTION

A rapidly growing area of interest in the field of computer technologyis that of “multimedia”. This term generally refers to the concurrentuse of video and audio in a computer system for a wide range ofapplications including business and entertainment.

The primary applications which have led to the tremendous success ofpersonal computers have been based on the power of these computers toprocess numbers in complex ways such as through spreadsheets, graphics,word processing and data bases. However, in such applications, theapplication program works with a discrete data file and typically workswith only a small part of such a data file at any one time. Multimediaapplications add a major new aspect to the processing of data bypersonal computer. This is the requirement to manage and process acontinuous stream of data as opposed to discrete data files which aretypically processed by an application program. The stream of dataassociated with a multimedia application is generally for too large tobe loaded in memory, and in many cases the data is continuous with nopredetermined end of the data. A further feature of multimedia streamingdata is that it is sequential in nature and frequently is timedependent, that is, it must not only be processed in a specificsequential order, it must also be processed to produce precisely timedsequential events.

An example of multimedia streaming data is the output which is producedby a DVD (Digital Versatile Disk) apparatus. The contemporary DVDapparatus produces data using the MPEG-2 video and audio format. Thisoutput actually comprises three separate data streams which are video,audio and subpicture. Each of these streams requires separateprocessing, but the results of the processing must be time synchronizedand generated at a predetermined absolute rate to obtain the desiredresults. Video and audio signals must be properly synchronized and timedto generate a viable multimedia presentation.

A standardized computer platform, including hardware and software, mustbe able to work with a large number of independently produced multimediaadapters, such as DVD players, video cameras, audio sources and ROMdiscs. Each of these products requires a separate, complex driver whichfunctions to interface application programs through the computeroperating system to the specific hardware in order to process themultimedia streaming data to produce continuous outputs. However, toaccommodate the massive amounts of data and the extensive, complexprocessing of this data required for a successful multimediaapplication, the driver must be highly efficient, well designed andcapable of performing a wide range of functions within the operatingsystem and functions required by the application program. With thegrowing complexity of operating systems and the greater demands ofapplication programs, it is very difficult for each independent producerof a hardware device, particularly for multimedia, to produce anefficient, current and effective driver for that product. Thus, thereexists a need to reduce the burden of producing drivers for multimediaproducts.

In other areas of computer system operation, such as for pointingdevices, for example, a mouse, it has been proposed to have a hardwareindependent driver associated with the operating system and have ahardware dependent driver provided by the hardware manufacturer for eachparticular device. See U.S. Pat. No. 5,465,364 entitled “Method AndSystem For Providing Device Driver Support Which Is Independent OfChangeable Characteristics Of Devices And Operating Systems”. Pointingdevices, however, do not have the same problems that are encounteredwith multimedia applications. The data rate for pointing devices isextremely low, the data processing is not particularly complex and thepointing device is generally a support aspect of an application program,in contrast to being an aspect that is a principle part of a multimediaapplication.

In view of the substantial problems encountered in the use of multimediaapplications on personal computers, and the insatiable consumer demandfor greater bandwidth and data processing sophistication, there is aneed for a multimedia driver configuration which can efficiently handlethe volume and complexity of streaming data while at the same timeminimizing the burden and difficulty of driver design for theindependent developers and manufacturers of multimedia products.

SUMMARY OF THE INVENTION

The present invention is a method of operation, and correspondingcomputer program units, for a stream class driver which is used inconjunction with a minidriver. The minidriver is associated with ahardware adapter which generates or receives streaming data. Theoperation of the stream class driver product begins with receiving ofinitialization data from the minidriver followed by registration of theinitialization data for later use by the stream class driver. Afterregistration, the stream class driver creates a device object for theadapter. The stream class driver then sends a command to the minidriverto initialize the adapter. Next, the stream class driver requests thatthe minidriver provide adapter stream information for all of the datastreams handled by the adapter. The minidriver provides this informationand the stream class driver registers the received adapter streaminformation. The stream class driver may then provide a command to theminidriver to turn off power to the adapter and then pages out theminidriver and subsequently awaits a data stream request.

Upon receipt of a data stream request, the stream class driver pages inthe minidriver to active memory. A command is generated to theminidriver to turn on power to the adapter. The stream class driverprovides a data stream open command and stream structure data to theminidriver as needed to open the data stream requested by an applicationprogram. Next, the stream class driver provides a stream read or asstream write command to the minidriver. Properties and controlinformation in a predefined data format related to the stream requestare transmitted from the stream class driver to the minidriver. Uponreceipt of a data stream termination command initiated by an applicationprogram, the stream class driver provides a stream close command to theminidriver. Finally, the stream class driver provides anuninitialization command to the minidriver for uninitializing theadapter.

In a further aspect of the present invention, the stream class drivercan open additional data streams for either reading or writing streamingdata concurrently with the first data stream.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of a portion of a computer system illustratingthe relationship of the streaming class driver in accordance with thepresent invention with an operating system, an application program, arelated minidriver and an adapter which is an apparatus which handlesstreaming data,

FIG. 2 is a flow diagram illustrating the initialization of thestreaming data adapter through functions carried out by the operatingsystem, the streaming class driver and the minidriver, and

FIG. 3 is a flow diagram illustrating the steps that are carried out,after initialization, for requesting and terminating a data stream inaccordance with the present invention.

DETAILED DESCRIPTION

The present invention includes a stream class driver for use in acomputer operating system. The purpose of this stream class driver is tomake the writing of hardware drivers (minidrivers) for streaming devicesmuch simpler. The functions performed by the minidriver are limited tothose functions which are unique or necessary for the associatedhardware, while the stream class driver performs all of the functionswhich are not dependent upon the particular hardware implemented.

Terminology

The principal terms used in describing the functions, data structures,commands and other aspects of the present invention are defined asfollows:

-   1. AC-3: An audio standard for delivering digital audio developed by    Dolby Laboratories.-   2. ActiveMovie: A cross-platform API developed by Microsoft    Corporation for developers of multimedia applications that provide a    user-mode connection and stream architecture to support high quality    digital video, high fidelity audio, and special effects, now termed    “Direct Show”.-   3. Adapter: a hardware device for generating, handling or consuming    streaming data-   4. API: Application Programming Interface—A set of routines that an    applications program uses to request and carry out lower-level    services performed by a computer operating system.-   5. CSA: Connection and Streaming Architecture—A functional    specification produced by Microsoft Corporation defining an    architecture and interface for application programs using streaming    data and synchronization tasks. This is kernel-mode streaming in    WDM.-   6. DLL: Dynamic Link Library—An API routine that user mode    applications access through ordinary procedure calls.-   7. DMA: Direct Memory Access-   8. Driver: Kernel Mode used to either control a hardware device or    to emulate a hardware device.-   9. EISA: Extended Industry Standard Architecture, a 32-bit bus    configuration developed as an extension of ISA.-   10. Filter: An entity which performs a specified function and    includes a collection of related connection points called pins-   11. GUID: Globally Unique Identifier. A quantity which is unique and    includes a current date/time and a sequence number and which is used    to allow any party to create an identifier which will not overlap    other identifiers similarly created.-   12. IEEE 1394: A standardized serial bus for high speed data    transfer.-   13. IOCTL: I/O control-   14. IRP: I/O Request Packet—Data structures that drivers use to    communicate with each other.-   15. IRQ: Interrupt Request—A method by which a device can request to    be serviced by the device's software driver.-   16. ISA: Industry Standard Architecture—legacy bus configuration for    original personal computer design.-   17. ISO: International Standards Organization-   18. ISR: Interrupt Service Routine-   19. Kernel Mode: The processor mode which allows full, unprotected    access to the system. A driver or thread running in kernel mode has    access to system memory and hardware.-   20. Minidriver: A hardware specific DLL that uses a class driver to    accomplish most actions through functional calls and provides only    device-specific controls.-   21. MPEG: Moving Pictures Expert Group—A standard for compression    and transmission of digital video.-   22. PCI: Peripheral Component Interconnect—A high-performance,    32-bit or 64-bit bus designed to be used with devices that have high    bandwidth requirements such as the display subsystem.-   23. Pin: A set of properties which describe a potential connection    point to a filter.-   24. PIO: Programmed input/output, which is much like a complement to    DMA.-   25. Plug and Play (PnP): An enumerator standard for automatically    detecting and recognizing installed hardware, as defined by    Microsoft Corporation-   26. SRB: Stream Request Block-   27. USB: Universal Serial Bus—A bidirectional, isochronous,    dynamically attachable serial interface for adding peripheral    devices such as game controllers, serial and parallel ports, and    input devices on a single bus.-   28. User Mode: The nonprivileged processor Mode in which application    code executes.-   29. VxD: Virtual Device Driver—A device driver that runs at the    privileged ring 0 protected Mode of the microprocessor.-   30. WDM: Windows 32 Driver Model—A 32 bit driver model based on the    Windows NT driver model that is designed to provide a common    architecture of I/O services and binary-compatible device drivers    for both Windows NT and Windows operating systems for specific    classes of drivers.-   31. Windows NT Driver Model: The layered device driver model used    under the Windows NT operating system (see “Inside Windows NT” by    Helen Custer (Microsoft Press 1993)).-   32. Windows NT: Refers to the Microsoft Corporation Windows NT    Version 4.0 operating system, including any add-on capabilities and    any later versions of the operating system.    Operational Description

The operating environment of the present invention is illustrated inFIG. 1. This drawing shows selected hardware and software within apersonal computer system which is preferably a system using an IntelCorporation x86 microprocessor and a Microsoft Corporation operatingsystem such as Windows NT. The present invention is used within theillustrated environment for supporting a multimedia application, such asan application program 20. The present invention is directed to a streamclass driver 22, which is preferably included within an operating system24. The application program 20 interacts with the operating system 24through an application programming interface (API) 26. The operatingsystem 24 includes the conventional features and operating aspects, notillustrated, which are well-known in the industry. A system bus driver28 is a part of the operating system 24 and is used to providecommunication through a bus 30, such as a PCI bus used with personalcomputers.

The upper edge of a stream class driver 22 of the present invention isaccessed through a CSA interface 32, which is defined in “Windows DriverModel Connection and Streaming Architecture Design Notes and Reference”,published by Microsoft Corporation. This document, which is incorporatedherein by reference, is a part of the “MEMPHIS” designated operatingsystem documentation entitled Windows 98 Developer's Release DeviceDriver Kit (DDK).

CSA interface 32 is further defined in U.S. patent application Ser. No.08/825,957, filed Apr. 4, 1997, entitled “Method And Computer ProgramProduct For Reducing Inter-buffer Data Transfers Between SeparateProcessing Components”, which is incorporated herein by reference.

The class driver 22 can be embodied in a computer readable medium suchas magnetic disk, optical disk or magnetic tape.

The lower edge connection to the stream class driver 22 is defined by astream class driver/minidriver interface 34, which is specified indetail herein and in the attached appendices.

A minidriver 36 communicates through the interface 34 with the streamclass driver 22. Minidriver 36 is a unique design corresponding to ahardware adapter 40. The adapter 40 is preferably a device thatgenerates or consumes streaming data, such as used in a multimediaapplication. An example of the adapter 40 is a DVD player which producesdigital audio and video streams for a motion picture.

Minidriver 36 is a hardware-specific DLL that uses the class driver 22to accomplish most actions through function calls, and provides onlydevice-specific controls. The minidriver 36 registers each adapter, suchas 40, with the class driver 22, and the class driver 22 creates adevice object to represent each adapter 40 that it registered. Thisprocess is described in more detail below. Minidriver 36 uses the classdriver's device object to make system calls.

The adapter 40 is connected to transmit and receive commands and totransmit and receive data through the bus 30. In a typicalimplementation, the application program 20 is a multimedia applicationthat uses streaming data provided by the adapter 40 through the bus 30.

Operating system aspect 42 includes the minidriver 36, which is uniqueto the adapter 40, but when implemented with a particular computersystem becomes a part of the operating system 24 of that computer.

The internal interface 34 between the class driver 22 and the minidriver36 is primarily a set of function calls between these drivers. The classdriver 22 controls the request flow, calling the minidriver 36 whenaccess to the adapter 40 hardware is necessary. The class driver 22 isresponsible for multiprocessor and interrupt synchronization. Once boththe class driver 22 and the minidriver 36 are initialized, theminidriver 36 is passive and is called only by the class driver 22. Mostof the function calls from the minidriver 36 to the class driver 22 arelow-level service requests.

The detailed description for the specific embodiment of the presentinvention presented herein includes the description in the appendicesthat follow. These are:

-   -   Appendix I Stream Class Driver Functions (Stream Class Driver        22)    -   Appendix II Minidriver Functions (Minidriver 36)    -   Appendix III Stream Request Block (Interface 34 SRB)    -   Appendix IV SRB Command Codes For the Adapter (Interface 34        Device Code)    -   Appendix V Stream Specific Command Codes (Interface 34 Stream        Command Code)

These appendices describe in detail the functions, data structures andcommands for the interface 34.

FIG. 2 illustrates the operation of the present invention in conjunctionwith the operating system 24 and minidriver 36 to initialize themultimedia aspects of the computer system in preparation for receiving adata stream request from application program 20. As shown in FIG. 2, thesteps of operation are divided in columns between the operating system24, stream class driver 22 and minidriver 36.

The operating system 24 functional operation begins at a start point 50.Next, step 52 is performed to power up the system and perform theconventional self tests which are well known in the personal computerindustry.

After the system has been powered up and the operating systeminitialization process is performed, step 54 is executed in which anenumerator, such as Plug n Play detects the attached adapter 40. Whenthe adapter has been detected, the Plug n Play enumerator, in step 56,loads into memory the minidriver 36 for the detected adapter 40. In step58, the Plug n Play initiates the minidriver 36 DriverEntry routine, asdescribed in Appendix II.

Further referring to FIG. 2, the next functional step carried out isperformed by the minidriver 36 in step 60. In this step the minidriver36 calls the class driver 22 function StreamClassRegisterAdapter. (SeeAppendix I) The minidriver 36 further collects and passes the datastructure termed HW_INITIALIZATION_DATA. This data structure isdescribed in detail in Appendix II.

From step 60, control is transferred to step 62, which is performed bythe stream class driver 22. Within step 62, the initialization dataprovided in the HW_INITIALIZATION_DATA structure is registered, that is,it is recorded in memory for use by the class driver 22. Next, in step64, the stream class driver 22 creates a device object corresponding tothe adapter 40. The minidriver 36 will not create a device object, butinstead will share the class driver 22 device object as needed. Only onedevice object is created per adapter.

In step 66, the stream class driver 22 calls the minidriver 36 toinitialize the adapter 40. This is done by calling the minidriver'sfunction HWReceivePacket with the command SRB_INITIALIZE_DEVICE. (SeeAppendix IV)

In step 68, the minidriver 36 initializes the adapter 40 hardware byperforming the required setup and loading in the adapter any coderequired for operation of the hardware.

In step 76, control is returned to the streaming class driver 22 whichcalls the minidriver 36 for stream information. This is done with thecommand SRB_GET_STREAM_INFO (Appendix IV), which is sent to theminidriver function HWReceivePacket.

Upon receipt of the SRB_GET_STREAM_INFO command, the minidriver 36 instep 78 builds a hardware stream descriptor for all streams that aresupported by the adapter 40. This information is returned to the classdriver 22. In step 80, the streaming class driver 22 registers thehardware stream descriptor in memory for future use.

Next, in step 82, the stream class driver 22 generates a power offcommand which is transmitted to the minidriver 36 for the adapter 40.(See Appendix IV) In general, the operating system 24, with driver 22,will turn off power to the adapter 40 whenever it is not being used,especially for battery powered computers.

The minidriver 36 receives the power off command in step 84 and turnsoff power to the adapter 40. In many systems, particularly portablecomputer systems, the adapter 40 is a device which uses a relativelysubstantial amount of electrical power. By disabling the adapter 40 whennot in use, system power will be conserved.

Control is returned to the stream class driver 22 in step 86 wherein thedriver 22 pages out the minidriver 36 program so that it is no longerstored in active memory, thus freeing resources for use by theapplication program 20, operating system 24 or other activeapplications. The device object is preferably closed, by closing itsfile handle, prior to paging out the minidriver 36. Finally, the classdriver 22 enters state 88 to wait for a stream request which requiresuse of the adapter 40.

Upon completion of the steps shown in FIG. 2, the computer systemmultimedia subsystem has been initialized and set to be ready to use theadapter 40 for streaming data when needed.

Referring to FIG. 3, there is shown a series of interrelated operationscarried out by the operating system 24, class driver 22 and minidriver36 after the multimedia subsystem has been initialized as shown in FIG.2. These operations are carried out to initiate and terminate a datastream request. A stream request 100 is generated by the operatingsystem 24 in response to the application program 20. The data streamrequest is provided to the stream class driver 22 which responds in step102 to page in the minidriver 36. This step loads the minidriver 36 intoactive memory. If the device object has been closed, it is opened priorto paging in the minidriver. If the minidriver 36 has not been pagedout, step 102 is not needed.

In step 104, the stream driver 22 sends a power on command to theminidriver 36 for the adapter 40. This command is received by theminidriver 36 and in step 106 it turns on power to the adapter 40 bytransmitting appropriate commands to the adapter 40 through the bus 30.Steps 104 and 106 are not needed if power has not been terminated to theadapter 40.

In step 108, the driver 22 calls the minidriver function HWReceivePacketwith the command SRB_OPEN_STREAM (Appendix IV) and further provides adata structure HW_STREAM_OBJECT. (See Appendix III) This data structureprovides the information needed by the adapter 40 and minidriver 36 toservice a stream command which will be received from the applicationprogram 20.

Upon receipt of the stream open command, the minidriver 36 performs step120 to activate the adapter 40 and open the specified stream. For thedescribed example wherein the adapter 40 is a DVD, the specified streamcould be the video stream. For other streams, such as audio, a newstream request 100 would need to be generated through the operatingsystem 24 by the application program 20.

When the step 120 has been confirmed, the class driver 22 sends either astream read (SRB_READ_DATA) or a stream write (SRB_WRITE_DATA) commandto the minidriver function ReceiveDataPacket, as specified in theHW_STREAM_OBJECT for the selected stream. The minidriver 36 receives andstores the read or write command at step 124.

In step 126, the class driver 22 sets properties and other controlinformation for the selected stream by passing the appropriate streamrequest block (SRB) to the minidriver's ReceiveControlPacket function asspecified in the HW_STREAM_OBJECT for the selected stream.

At step 128, the minidriver 36 sets the properties and controlinformation received for the selected data stream so that the datastream transfer proceeds as requested by the application program 20. Atthis point, the minidriver 36 is responsible for the streaming datarequest until it notifies the class driver 22 that the request has beencompleted.

In state 130, the class driver 22 waits for receipt of a streamtermination command while the streaming data transfer proceeds betweenadapter 40 and application program 20.

When the application program 20 has completed use of the specified datastream, a stream termination 150 command is generated by the operatingsystem 24 and transferred to the class driver 22 at step 152. In thisstep, the stream class driver 22 calls the minidriver 36 and sends astream close command, SRB_CLOSE_STREAM, to the minidriver'sHWReceivePacket function. In response to this command, the minidriver 36at step 153 closes the specified stream. The transfer of data for thecurrent stream is completed at an end state 154. After step 153, theclass driver 22 may, optionally, close the device object, page out theminidriver 36, and turn power off to the adapter 40.

When the operating system 24 detects at step 155 that the adapter 40 hasbeen disabled by the user, physically removed, or the system is beingshut down, control is transferred to the driver 22 at step 156 in whichthe driver 122 calls the minidriver 36 and sends an uninitializationcommand SRB_UNINITIALIZE_DEVICE. In step 158 the minidriver 36 performsthe actions needed to uninitialize the adapter 40. The actions requiredare dependent upon the particular design of the adapter 40, and willvary from one manufacturer to the next. After the adapter 40 has beenuninitialized, the minidriver 36 operation terminates at the end state160.

While a streaming data request is being processed, the streaming adapter40 may generate interrupts. When an interrupt is detected, the classdriver 22 will call the minidriver 36 interrupt service routine, asdescribed in Appendix II. All of the minidriver 36 functions aresynchronized with the adapter 40 ISR. This is done to make theminidriver 36 nonreentrant. Nonreentrancy is accomplished by masking offthe IRQ of the adapter 40 (and all lower priority IRQs) when code isbeing executed in any of the minidriver 36 routines. When a thread isexecuting in the minidriver 36, no calls will be made to any otherfunction within the minidriver 36, including the ISR. This nonreentrancyholds true even on multiprocessor systems, making the minidriver 36 veryeasy to write.

Due to routine synchronization and request serialization, the minidriver36 is multiprocessor safe and nonreentrant for low-to-medium-endhardware. The processing described above has correct file operationsynchronization. For example, stream and adapter 40 opens are correctlyserialized without having the minidriver 36 implement mutexes,semaphores, or events. AU low-level buffer management is handled by theclass driver 22. This includes allocation of DMA adapter object, asnecessary, mapping of buffers and building scatter/gather list for DMA,and locking and flushing buffers appropriately in DMA versus PIO cases.All IOCTL parameter validation is performed by the class driver 22. Allrequests are timed by the class driver 22 with a watchdog timer.

A particular advantage for the class driver 22 of the present inventionis that it can work with a wide variety of streaming hardware devicessuch as MPEG, video capture, USB audio and video and IEEE 1394 audio andvideo.

In summary, a driver configuration for streaming data includes a streamclass driver for performing system operations which are independent ofthe streaming data adapter and a minidriver which performs a minimum setof functions that are dependent upon the specific hardware designimplemented for the adapter. As a result, the minidriver design isgreatly simplified and can be more easily implemented for each of alarge number of streaming class devices.

Although one embodiment of the invention has been illustrated in theaccompanying drawings and described in the foregoing DetailedDescription, it will be understood that the invention is not limited tothe embodiment disclosed, but is capable of numerous rearrangements,modifications and substitutions without departing from the scope of theinvention.

1. A method of operation for a stream class driver which functions inconjunction with a minidriver that is associated with a particularhardware adapter which generates or receives streaming data, wherein thestream class driver implements one or more system operations that areindependent of any particular hardware adapter, and wherein theminidriver implements one or more operations that depend on theparticular hardware adapter's design, the method comprising, after saidadapter has been initialized and said minidriver has been paged out ofactive memory to free resources for other uses, the stream class driver:paging said minidriver into active memory upon receipt of a data streamrequest in preparation for using one or more routines implemented by theminidriver for the particular hardware adapter, providing a command tothe one or more routines implemented by said minidriver to turn on powerto said adapter, providing a data stream open command and streamstructure data to the one or more routines implemented by saidminidriver, providing a stream read or write command to the one or moreroutines implemented by said minidriver, providing properties andcontrol information related to said stream request to the one or moreroutines implemented by said minidriver, providing a stream closecommand to the one or more routines implemented by said minidriver uponreceipt of a data stream termination command, and providing anuninitialization command to the one or more routines implemented by saidminidriver for uninitializing said adapter.
 2. A method of operation fora stream class driver as recited in claim 1, wherein said data stream isa video data stream.
 3. A method of operation for a stream class driveras recited in claim 1, wherein said data stream is an audio data stream.4. A method of operation for a stream class driver as recited in claim1, further comprising the following performed by the stream class driverprior to providing an uninitialized command to said minidriver:providing a second data stream open command and second stream structuredata to said minidriver upon receipt of a second data stream request,providing a second stream read or write command to said minidriver,providing properties and control information related to said secondstream request to said minidriver, wherein said first and second datastreams are opened concurrently, and providing a second stream closecommand to said minidriver upon receipt of a data stream terminationcommand for said second data stream.
 5. A computer program productcomprising: a computer usable medium having computer readable programcode means embodied therein for a stream class driver which functions inconjunction with a minidriver that is associated with a particularhardware adapter which generates or receives streaming data, wherein thestream class driver implements one or more system operations that areindependent of any particular hardware adapter, and wherein theminidriver implements one or more operations that depend on theparticular hardware adapter's design, and wherein said adapter has beeninitialized and said minidriver has been paged out of active memory tofree resources for other uses, the computer readable program code meansfor the stream class driver in said computer program product comprising:computer readable program code means for paging said minidriver intoactive memory upon receipt of a data stream request in preparation forusing one or more routines implemented by the minidriver for theparticular hardware adapter, computer readable program code means forproviding a command to the one or more routines implemented by saidminidriver to turn on power to said adapter, computer readable programcode means for providing a data stream open command and stream structuredata to the one or more routines implemented by said minidriver,computer readable program code means for providing a stream read orwrite command to the one or more routines implemented by saidminidriver, computer readable program code means for providingproperties and control information related to said stream request to theone or more routines implemented by said minidriver, computer readableprogram code means for providing a stream close command to the one ormore routines implemented by said minidriver upon receipt of a datastream termination command, and computer readable program code means forproviding an uninitialization command to the one or more routinesimplemented by said minidriver for uninitializing said adapter.
 6. Acomputer program product as recited in claim 5, wherein the computerreadable program code means for the stream class driver furthercomprises: computer readable program code means for providing a seconddata stream open command and second stream structure data to saidminidriver upon receipt of a second data stream request, computerreadable program code means for providing a second stream read or writecommand to said minidriver, computer readable program code means forproviding properties and control information related to said secondstream request to said minidriver, wherein said first and second datastreams are opened concurrently, and computer readable program codemeans for providing a second stream close command to said minidriverupon receipt or a data stream termination command for said second datastream.